Multilayer composite armour

ABSTRACT

The invention relates to the area of armor and in particular to multilayer armor having a composite layer containing a first material made of a metal or an alloy and a second material where the second material is porous and in that the metal or metal alloy is infiltrated into some or all of the pores of the second material and characterized in that a cage made of plates having openings contains the first and second materials and in that the cage is itself coated, at least partly, with the infiltration metal or alloy, the melting point of the cage material being higher than that of the infiltration metal or alloy.

BACKGROUND OF THE INVENTION

The invention relates to the area of armor and in particular multilayerarmor having a composite layer containing a first material, for examplea ceramic, and a second material, such as a metal or metal alloy.

Ceramic has been known for its ballistic performance for a number ofyears, either as a material placed at the front face of a piece of armoror embedded in the metal material to increase overall armoreffectiveness.

The most significant work in the area of cast composite armor hasrelated mainly to production of armor with a series of ceramicreinforcements distributed in a metal matrix, generally obtained by aprocess related to casting.

These types of armor, although their performance is satisfactory, aregenerally difficult to fabricate and do not have guaranteed protectioneffectiveness that is identical for all angles of attack, for all impactpoints on the front face, and also have low performance with multipleimpacts (two successive shots striking the same impact zone).

Moreover, in view of the nature and shape of the reinforcement bodiesused, and in view of the implementation difficulties, the cost of theprotection thus obtained is generally high by comparison to armorcomposed of monolithic materials.

Finally, the exceptional compressive strength performance of ceramics isnot fully exploited due to the confinement configurations recommended bythe various inventors, which do not exhibit an optimal configuration.

For example, McDougal et al., in their U.S. Pat. No. 3,705,558, providea light armor composed of a layer of ceramic balls placed in contact butsuch that a small gap between the balls allows for a liquid metalcoating to pass through. Various configurations are then possible, suchas, the ceramic balls are enclosed in a stainless steel pouch, or theyare covered with a nickel layer and then attached to an aluminum plate.The technique proposed by McDougal et al. has been criticized for itsimplementation difficulty and the risk inherent in the process ofdamaging the ceramic by thermal shock during the liquid metal coatingphase. Moreover, in the casting phase, the technique recommended byMcDougal et al. sometimes leads to unwanted movement of one ballrelative to another. This unexpected movement affects armoreffectiveness locally, and for this reason U.S. Pat. No. 4,158,338describes a strong wall panel containing hard, and thus, nonporousceramic particles, disposed during manufacture in a cage that holds themin position, and having holes through which is injected a liquefiedelastomer whose temperature is unable to damage the ceramic particles.U.S. Pat. No. 4,534,266, which describes a method of obtaining a regularnetwork of interconnected metal spheres that receive ceramic insertssubsequently embedded by the liquid metal during the casting stage, isalso known.

Other patents, such as, for example, U.S. Pat. No. 5,194,202, U.S. Pat.No. 4,415,632, DE 3924267, and DE 3837378 describe armor having acomposite layer containing a first material composed of a metal or metalalloy and a second material and characterized in that the secondmaterial is porous and in that the metal or the alloy is infiltratedinto all or some of the pores of the second material.

However, such an armor cracks when struck by a projectile and when otherplates made of metal, for example, are associated therewith by cementingor welding, separations occur between the plates which is detrimental tothe integrity and strength of the whole or the welds break due to shearforces, leading once again to a reduction in the integrity and strengthof the whole.

SUMMARY OF THE INVENTION

The goal of the invention is to remedy the aforesaid difficulties byproviding a light, effective armor that is easy to fabricate, hasunparalleled integration flexibility, and has no weaknesses in integrityor strength in the event of cracking of the composite layer.

The solution provided is a multilayer armor having a composite layercontaining a first material made of a metal or an alloy and a secondmaterial where the second material is porous and the metal or the metalalloy is infiltrated into some or all of the pores of the secondmaterial, wherein a cage made of plates having openings contains thefirst and second materials and in that the cage itself is coated, atleast partly, with the infiltration metal or alloy, the melting point ofthe cage material being higher than that of the infiltration metal oralloy.

According to another additional feature, the cage is entirely coatedwith the infiltration metal or alloy.

According to another feature, the void ratio of the ceramic is between0.1% and 80%.

According to another feature, the ceramic is partly or entirelycomprised of at least one of the following ceramics: recrystallized SiCand/or other types of ceramics, such as SiC—SiN, SiC—SiO₂, SiN, Al₂O₃,AlN, and Si₃N₄.

According to a particular feature, the ceramic is partly or entirelycomprised of recrystallized silicon carbide.

According to another feature, the cage contains several superimposed orjuxtaposed reinforcing bodies made of infiltrated porous ceramic.

According to another feature, the cage is made of metal or alloy.

According to a particular feature, the cage is made partly or entirelyof one of the following metals or their alloys: iron, steel, copper,zinc, aluminum, magnesium, beryllium, or titanium.

According to one feature, the metal or the alloy infiltrated into thepores of the ceramic is made partly or entirely of aluminum, magnesium,beryllium, or titanium.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features of the invention will appear in thedescription of various embodiments of the invention with reference tothe attached figures:

FIG. 1 is a perspective view of one example of a porous reinforcing bodydesigned to enter into the composition of armor according to theinvention;

FIG. 2 is a perspective view of one example of a metal cage designed tocontain the porous reinforcing body;

FIG. 3 is a vertical section through a first embodiment of armor inwhich the porous reinforcing body forms only one body in the cage;

FIG. 4 is a vertical section through a second embodiment of armorcontaining several juxtaposed porous reinforcing bodies;

FIG. 5 is a vertical section through a third embodiment of armorcontaining several superimposed porous reinforcing bodies;

FIG. 6 shows one application of the invention for protection of aperson;

FIG. 7 shows one application of the invention to a vehicle forprotection of its occupants; and

FIG. 8 shows one application of the invention to an armored vehicle forprotection of its occupants.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of an example of a body 1 made of porousreinforcing material designed to enter into the composition of thearmor. This body 1 is parallelepipedic in shape and is a ceramic. It ismade of recrystallized silicon carbide. Its void ratio is 15%. This bodyhas two large transverse surfaces 2 and small lateral surfaces 3.

FIG. 2 is a perspective view of an example of a metal cage 4 designed toenclose said body 1 made of porous reinforcing material. This cage 4 iscomposed of steel plates 5 having regularly disposed circular openings6. These plates 5 are welded together to form a cage 4 inside which thebody 1 made of porous reinforcing material can be positioned, at leastone of the faces of the parallelepiped being welded once the porous body1 has been placed inside cage 4.

The dimensions of the cage 4 and the porous body 1 are such that thereis several millimeters or even more of play between one of thetransverse faces 2 of the porous body and the corresponding insidelateral face of cage 4. On the other hand, the play is practically zerobetween the lateral surfaces 3 of porous body 1 and the correspondinginside surfaces of cage 4.

FIG. 3 is a vertical section through an example of armor 19 wherein theface exposed to the munition is called the front face 10 while theopposite face 12 is called the rear face.

The armor 19 is of the multilayer composite type. It has a first layer13 that is thin—several millimeters—and made of infiltration metal, inthis case aluminum, then a composite 15 layer comprised of a cage 14containing a porous reinforcing body 11 made of recrystallized siliconcarbide infiltrated and coated with the infiltration metal, and finallya third layer 16 that is thick—several centimeters—consisting ofinfiltration metal.

It will be noted that the porous ceramic infiltration metal not onlyinfiltrates the pores of the ceramic but also coats the composite 15,the thickness of this coating being small on the front face 10 and thelateral faces 17 of cage 14 and thick on the rear face 12 of the armor.

FIG. 4 is a vertical section through another example of an armor 29according to the invention.

The face exposed to the munition is called the front face 20 while theopposite face 22 is called the rear face.

This armor 29 is of the multilayer composite type. It has a first layer23 that is thin—several millimeters thick—and made of infiltrationmetal, in this case magnesium, then a composite comprised of a cage 24containing several juxtaposed porous reinforcing bodies 21 made ofalumina Al₂O₃ infiltrated and coated with the infiltration metal, andfinally a third layer 16 that is thick—several centimeters—consisting ofinfiltration metal.

FIG. 5 is a vertical section through another example of an armor 39according to the invention.

The face exposed to the munition is called the front face 30 while theopposite face 32 is called the rear face.

This armor 39 is of the multilayer composite type. It has a first layer33 that is thin—several millimeters thick—and made of infiltrationmetal, in this case titanium, then a composite comprised of a cage 34containing several superimposed porous reinforcing bodies 31, one madeof recrystallized silicon carbide with a void ratio of 21% and the otherof Si₃N₄ with a void ratio of 11%, both being infiltrated and coatedwith the infiltration metal, and finally a third layer 36 that isthick—several centimeters—made of infiltration metal.

The components entering into the fabrication of the invention aredeliberately chosen from the family of mass-produced industrial productsto attain the objective of low cost while meeting the objectives ofperformance, weight, ease of integration, and resistance tomulti-impacting presented above.

Thus, the material of the porous ceramic reinforcing body may, forexample, be recrystallized silicon carbide (SiC) but also other types ofceramics, such as SiC—SiN, SiC—SiO₂, SiN, Al₂O₃, AlN, and Si₃N₄. Theporosity of the reinforcing body must enable the infiltration metal topenetrate most or all of the pores to create an intimate bond betweenthe two components and establish a state of local residual stressesgenerated by the differences in coefficient of thermal expansion betweenthe ceramic and the infiltration metal. Because the coefficient ofthermal expansion of the ceramic is extremely low (a few 10⁻⁶/K), theceramic material infiltrated by a metal (whose expansion coefficient isbetween 2 and 10 times higher) has its expansion coefficient fixedalmost solely by the ceramic, which generates internal stresses in thematerial. The void ratio may typically be about 10 to 20%, but goodperformance may also be achieved with lower void ratios, typically 10%and down to values less than 0.1%, or, on the contrary, higher such as20 to 40%, for example. The void ratio, as explained above, is directlylinked to the level of internal stresses reached in the ceramic afterinfiltration by the metal and is, hence, to some degree linked to theballistic performance of the armor when impacted by a given munition.The armor will thus be optimized for a specific aggressor by choosingthe most suitable void ratio.

The reinforcing material is contained in a cage. This cage is made of asteel-type metal alloy so that it is easy to fabricate (in particularthe material is weldable) and inexpensive. However, other metals, suchas copper, zinc, iron, aluminum, magnesium, beryllium, or titanium oranother other similar metal or an alloy of these metals, can be used forfabricating the cage as long as the chemical and physicalcompatibilities between the reinforcing material, the cage, and theinfiltration metal permit. The cage must be designed to contain thereinforcing material and easily enable passage of the liquid metalduring the infiltration phase. Further, the melting point of thematerial of which the cage is made must be greater than the meltingpoint of the infiltration metal or alloy.

The cage has a dual role. During the armor fabrication phase, the cageenables the reinforcing material to be located in one part of the mold,and prevents the reinforcing material from cracking by a confinementeffect when the armor is impacted by the munition. When a projectilestrikes the ceramic/metal or alloy composite, the latter may be cracked;the presence of the plates of which the cage is made limits expansion ofthe composite, hence the likelihood that it will crack is reduced, andeven if it should crack, the cage deflects the crack, propagating it tothe nearest opening in the cage. Thus, cracking is very limited and theintegrity of the armor is unimpaired.

It should be noted that for deflection of the crack to occur, the ratiobetween the surface areas of openings 6 to that of the cage 4, namelyits front, rear, and lateral faces, must be less than 75%.

The infiltration material is preferably a low-density metal or an alloyof the low-density metal, such as aluminum, magnesium, or beryllium,but, for certain armor configurations, it may be useful to employ othermetals or alloys of these metals.

The invention calls for the cage containing the reinforcing material tobe fully embedded in the infiltration material. It is preferable tolocate the cage containing the reinforcing material near the front faceof the armor (namely the face supposed to undergo impact by themunition) while taking care to provide a thin layer of infiltrationmaterial between the armor surface and the cage. The armor may bedesigned with a fairly large volume of infiltration material at the rearface (namely the side opposite the side attacked) so that this materialcan deform by a plastic deformation process and eventually absorb theincident energy of the projectile.

The armor presented here is made by any known infiltration process suchas for example squeeze casting, casting, and pressure infiltration(plunger or gas). In all these processes, the infiltration material isfirst heated to melting point to acquire sufficient fluidity and is thenplaced in the presence of the cage containing the reinforcing material.Pressure application, and preheating the reinforcing material, are twomethods of facilitating infiltration of the metal into thereinforcement.

One method of manufacturing armor 19 according to the invention can bethe following:

aluminum metal is heated in a furnace until the metal melts;

a metal cage is prepared in two weldable steel half-shells provided withmany holes;

a porous recrystallized SiC ceramic plate is cut to dimensions slightlyless than those of the cage;

the SiC ceramic plate is inserted into the cage then closed with severalweld spots;

the cage+SiC ceramic plate assembly is preheated in a furnace;

the cage+SiC ceramic plate assembly is inserted into a squeeze castingmold;

liquid metal is poured over the cage+SiC ceramic plate assembly andpressure is applied to facilitate penetration of the liquid metal intothe pores of the SiC ceramic plate and through the cage;

the assembly is cooled under controlled-temperature conditions; and

the assembly is unmolded.

This process has also been used to make an armor plate according to theinvention with the goal of protecting part of a light vehicle. Thereinforcing material used is in the form of three porous ceramic plateswhose specifications are given below:

-   -   Type of ceramic: recrystallized silicon carbide (SiC);    -   Density: 2.6 to 2.7 g/cm³;    -   Void ratio: 15 to 19%;    -   Tensile strength at 20° C.: 90 to 100 Mpa;    -   Tensile strength at 1300° C.: 100 to 110 Mpa;    -   Young's modulus: 230 Gpa;    -   Thermal conductivity: 30 W/m/K;    -   Coefficient of thermal expansion: 10⁻⁶/K; and    -   Plate size: 150 mm×75 mm×8 mm.

This ceramic is a widely available product used, in particular, as anabrasion material for milling industrial tools.

The cage is obtained by bending and welding a 2 mm thick weldable steelsheet provided with circular holes. The dimensions of the cage are 152mm×77 mm×26 mm so that it can accept the three ceramic plates.

The infiltration material used is a classical foundry alloy of thealuminum-silicon type. The technique used for the casting phase issqueeze casting.

Armor according to the invention can be dimensioned to protect a persondirectly when used, for example, as a bullet-proof vest and as a helmetas shown in FIG. 6, or to protect land systems such as wheeled vehicles,tracked vehicles, shelters, infrastructures, movable bridges, etc. asshown in FIGS. 7 and 8, or flying craft such as airplanes, helicopters,drones, missiles, etc., or marine systems such as surface ships,submarines, crossing equipment, etc. against all types of projectiles,fragments, and shards.

The invention thus includes any type of composite armor and ballisticarmor containing one or more porous ceramic bodies enclosed in a metalcage, the entire assembly being infiltrated with a metal.

Depending on the application in view, the dimensioning of the solutionmay combine variants of the following parameters:

-   -   nature of infiltration metal material;    -   nature of porous reinforcing material;    -   nature of metal material of which the cage is composed;    -   dimensions of porous reinforcing material;    -   number of elements of porous reinforcing material enclosed in        the cage;    -   dimensions of cage (thickness of cage walls may be infinitely        small);    -   proportions of the various components in terms of weight and        volume; and    -   armor geometry (may be parallelepipedic, curved, tubular, or        other).

Several elements must be taken into consideration to illustrate thevalue of the invention.

First, a weight advantage. The components of the invention enable thearmor to be ranked as light armor comparable in performance to thereference aluminum armor (7020 alloy). Traditional protection solutionsfor light vehicles, such as automobiles, combat vehicles, transportvehicles, airplanes, helicopters, etc., employ panels severalmillimeters thick made of steel or titanium, and are hence heavier thanthe proposed solution.

The second advantage resides in the performance of the invention againstan extensive threat range. Of course, depending on the formulation usedfor the armor, it can be tailored to the type of threat by adjusting theweight-performance ratio. However, for a standard formulation, such asthat referred to above, the armor plate provides total protectionagainst projectiles of any weight with impact velocities of 500 to 1000meters/second. Moreover, this formulation is well below the 40 to 100kg/m² range. This range corresponds to the weight of the protectiveequipment normally used on light vehicles.

The third advantage has to do with the integration flexibility of theinvention. In its standard formulation, the armor can assume all theusual integration configurations of classical armor, namely:

the armor can be “applied,” i.e. applied to the structure to beprotected by any classical method, such as welding, cementing, bolting,adhesion, etc., as shown in FIG. 8;

the armor can be built directly into the structure for parts made by acasting method such as openers, hoods, bodies, fenders, doors, roofs,floors, wheel rims, etc., as shown in FIG. 7; and

in the case of the “bullet-proof vest” or “flexible armor” typeapplications, the protection can easily be integrated into a classicalgarment configuration by a mosaic of plates, as shown in FIG. 5.

The fourth advantage of the invention is cost-related. The inventionuses low-cost components and a low-cost manufacturing technique andprocedure enabling mass production with no particular productionconstraints.

The fifth advantage resides in the ability of the invention to providetotal protection even in the case of successive impacts on a singlearmor area (multi-impacting).

With regard to the particular case of flexible armor of the“bullet-proof vest” type as described for example in U.S. Pat. Nos.4,090,005 and 5,972,819, it is known that for the highest aggressionlevels the risks of injury are high for the wearer of the protectioneven though the munition is stopped. This damage is due to the effectsof indentation of the vest into the body, caused by insufficientdistribution of the impact force over the surface. The present inventionlimits these risks of rear-face damage by distributing the impact forcewidely.

Of course, numerous modifications may be made to the embodiment exampledescribed above without departing from the framework of the invention.Thus, a metal cage with an extremely small wall thickness may be used,and the same metal or metal alloy may be chosen for the infiltrationmaterial and for the cage.

1. Multilayer armor, comprising: a first material where the firstmaterial is porous; a second material comprising a metal or a metalalloy; and a cage made of plates having openings, wherein the firstmaterial is mounted in the cage and the second material passes throughthe openings to infiltrate some or all of the pores of the firstmaterial and coats the cage, at least partly, with the second material,the melting point of the cage being higher than that of the secondmaterial.
 2. Armor according to claim 1, wherein the cage is entirelycoated with said second material.
 3. Armor according to claim 2, whereinthe cage has two principal faces and four lateral faces, wherein thethickness of the coating of the second material is greater on one of theprincipal faces than on the other principal face and greater than on thelateral faces.
 4. Armor according to claim 3, wherein the thickestcoating thickness is a few centimeters.
 5. Armor according to claim 4,wherein the coating thickness on the lateral faces and on one of theprincipal surfaces is a few millimeters.
 6. Armor according to claim 4,wherein the ratio between the surface area of openings to that of thecage is less than 75%.
 7. Armor according to claim 6, wherein saidsecond material is comprised of a ceramic whose void ratio is between0.1% and 80%.
 8. Armor according to claim 7, wherein the ceramic ispartly or entirely comprised of at least one of the following ceramics:recrystallized (SiC) and other ceramics including SiC—SiN, SiC—SiO₂,SiN, Al₂O₃, AlN, and Si₃N₄.
 9. Armor according to claim 3, wherein thecoating thickness on the lateral faces and on one of the principalsurfaces is a few millimeters.
 10. Armor according to claim 3, whereinthe cage is made partly or entirely of one of the following metals ortheir alloys comprised of iron, steel, copper, zinc, aluminum,magnesium, beryllium, or titanium.
 11. Armor according to claim 2,wherein the ratio between the surface area of openings to that of thecage is less than 75%.
 12. Armor according to claim 11, wherein the cageis made partly or entirely of one of the following metals or theiralloys comprised of iron, steel, copper, zinc, aluminum, magnesium,beryllium, or titanium.
 13. Armor according to claim 11, wherein saidmetal or said alloy infiltrated into the pores of the first material ismade partly or entirely of a material comprised of aluminum, magnesium,beryllium, or titanium.
 14. Armor according to claim 1, wherein saidfirst material is comprised of a ceramic whose void ratio is between0.1% and 80%.
 15. Armor according to claim 14, wherein the ceramic ispartly or entirely comprised of at least one of the following ceramics:recrystallized (SiC) and ceramics to include SiC—SiN, SiC—SiO₂, SiN,Al₂O₃, AlN, and Si₃N₄.
 16. Armor according to claim 14, wherein theceramic is partly or entirely comprised of recrystallized siliconcarbide.
 17. Armor according to claim 16, wherein the cage containsseveral superimposed or juxtaposed reinforcing bodies made of theceramic.
 18. Armor according to claim 1, wherein the cage containsseveral superimposed or juxtaposed reinforcing bodies made of theceramic.
 19. Armor according to claim 1, wherein the cage is made partlyor entirely of one of the following metals or their alloys comprised ofiron, steel, copper, zinc, aluminum, magnesium, beryllium, or titanium.20. Armor according to claim 1, wherein said metal or said alloyinfiltrated into the pores of the second material is made partly orentirely of a material comprised of aluminum, magnesium, beryllium, ortitanium.